Pulse code modulation (PCM) is a sampling technique used for converting analog signals, usually audio signals, to digital signals. Although there are more efficient conversion techniques, for example, MPEG 1/2 audio layer 3 (MP3), the telecommunications industry, especially, still maintains and operates legacy systems that utilize PCM for converting analog voice signals to digital signals for transmission over circuit switched networks, whether local or long distance. The PCM standard utilizes a sample rate of 8000 samples per second and generates twelve to thirteen bits of linear digital data output per sample, which is then mapped via a logarithmic compression algorithm to an eight bit output. This mapping results in 64 Kbits of PCM voice data per second.
There are two algorithms that are widely used in the telecommunications industry for compressing linearly digitized voice—A Law and Mu Law. The Mu Law algorithm is used primarily in North America and the A Law algorithm is used in most of the rest of the world. The logarithm compression algorithms are utilized because the wide dynamic range of speech makes it inefficient to use linear digital encoding. By effectively reducing the dynamic range of a speech signal using algorithmic encoding, the speech signal to noise ratio is increased with respect to the linear digital sample and the smaller data size makes data transfer more efficient.
In some conventional systems, which are utilized for processing audio signals, a sudden change in volume from high to low or vice versa, may introduce annoying noises to the listener. These noises, sometimes described as clicks or pops, may also occur during startup or stoppage of playback of audio. On startup, when the speaker is at zero level, a sudden large input of data will produce a glitch which translates to a popping or clicking sound. Similarly, when playback is stopped, if the last data is a large value, the result can be a popping or clicking sound.
Some conventional systems attempt to remove these noises but in doing so introduce an added delay which is very noticeable when switching channels. Some television sets, for example, exhibit this problem when tuning to a new channel. There may be video output, but audio may be muted during a duration when the noises may be exhibited. Some other conventional systems, cable TV decoder or set-top boxes, for example, may stop the output of video and audio signals for the new channel, then use a software algorithm to try to remove the annoying noises, and then continue the output of video and audio signals.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.